There has heretofore been known thermoelectric materials of a type which comprise conductive layers and barrier layers in the form of very thin films having the same thickness (see, for example, U.S. Pat. No. 5,436,467).
In the thermoelectric material, the energy gap in the barrier layer is maintained to be much wider than the energy gap in the conductive layer to create a large difference between the two energy gaps, whereby quantum wells are formed in the conductive layers. As a result, the electric conductivity of the thermoelectric material is heightened, and an improved thermoelectric performance is exhibited.
Here, if a first semiconductor of the conductive layer and a second semiconductor of the barrier layer are mixed together in a boundary region between the barrier layer and the conductive layer at the step of forming the layers, the effect of the mixing readily appears on the barrier layer which is in the form of a very thin film. As a result, the energy gap is narrowed in the barrier layer, and the difference between the two energy gaps so decreases that no quantum well is formed in the conductive layer.
In order to strictly control the interface between the barrier layer and the conductive layer, therefore, the layers have heretofore been formed by a molecular beam epitaxial method (MBE), an atomic epitaxial layer method (ALE) or the like method.
However, currently available methods for controlling the interface between the barrier layer and the conductive layer have numerous shortcomings. For example, the above-mentioned methods require very expensive equipment and very complex process control. In addition, despite the control of the steps, the occurrence rate of defective products is high, resulting in an increase in the cost at which the thermoelectric materials are produced.
A need therefore exists for a thermoelectric material which has an excellent thermoelectric performance, and which increases the productivity and reduces the cost of production. The present invention fulfills these needs, and provides further related advantages.